The freezer compartment, which I never have anything stored in, at the top of the inside of my under-counter fridge has, for over a year now, been icing up faster than it should, including, significantly, around and on the outside of the door, jamming it shut, requiring defrosting about once a month—it is not an auto-defrost model. It means that the temperature of the main part of the fridge (ie, for chilled food) starts getting maintained at 10–15 °C; I then defrost. I hated defrosting when the fridge was functioning as it should, so it's even more of a chore now. I noticed that the bulk of the ice building up around the pull-down freezer door was at the left side of it, where there was an approximately 1 mm vertical gap, so I made a washer out of some scrap plastic to put at the other side on the spindle that acts as the hinge and that closed the gap. However, it's still icing up too fast. I took out the mechanical thermostat and tested it with a multi-meter and it switched its continuity current on an off okay. I also tested it by inserting the thermostat probe between the door seal and case of a separate, properly working stand-alone freezer I have and the stat clicked "off" after about maybe five minutes, and then clicked "on" when I removed it. I was unable to take an accurate temperature when it did this but I had set the stat knob to half-way. I have checked the rubber door seal and there is nothing wrong with it. I'm tempted to buy an electronic thermostat (eg: https://www.ebay.co.uk/itm/324618133446) to switch the fridge on and off at its 13 A plug. The fridge is a Beko model and must be at least twenty years old.